a. Field of the Invention
The present invention relates to a method of preparing NC (numerical control) tapes for NC machine tools.
B. Description of the Prior Art
NC machine tools (NC machines) are highly efficient and have spread in the industry as a hope for labor saving.
In operating an NC machine, however, an NC tape is required by which the operating commands are put in.
The preparation of NC tapes not only needs expert knowledge and a special language but also takes much time.
In the case of production of articles in small quantities, the total man-hour required for preparation of an NC tape can be greater than that required for machining of articles, often causing an increase in cost or a decrease in the rate of operation of the NC machine.
In general, the NC machine consists of a machine tool proper and a control unit for controlling the same, and, in many cases, different manufacturers produce different types of such machine tools and control units and employ different data input systems for the latter. Accordingly, various formats for NC tapes are now in use.
As a result, running two or three or more NC machines of different manufacturers will entail very cumbersome preparation of NC tapes.
The method of preparing NC tapes can be classified into manual programming and automatic programming.
Manual programming is the process of planning a sequence of machining steps from a design drawing, designing a jig, and preparing a process sheet. This operation is done by a programmer. In the phase of planning machining steps, selection of an NC machine and locations on work to be machined is effected. In the phase of preparing a process sheet, the contents of machining, machining sequence, tools to be used and conditions for machining are determined and coordinate calculations in the direction of depth are made. The values thus found are thus converted into coordinates for use in the NC machine, and the path and move of the tool are entered in the process sheet using the NC machine format. A key puncher punches a tape to record the contents of the process sheet thus prepared, thereby preparing an NC tape.
Manual programming is liable to cause errors, since the symbols and coordinate values in the direction of depth differ with each NC machine. Also, since the method of giving coordinate commands differs with each NC machine, errors will occur. Moreover, since the format differs with each NC machine, misentry often occurs, and so does mispunching.
In brief, manual programming necessitates manually carrying out complicated calculations and other program-making operations, thus requiring much time and labor, so that it is inefficient and does not necessarily provide a highly reliable program.
Automatic programming is the process of planning a sequence of machining steps from a design drawing, designing a jig, and preparing a process sheet and a part program. This operation is done by a programmer. The machining step planning and jig designing are the same as in manual programming. In the phase of preparing a process sheet, the contents of machining, machining sequence, tools to be used, conditions for machining and locations on work to be machined are defined and the path and move of the tool are described in the part program in a unique language.
A key puncher punches a card to record the contents of each part program thus prepared, thereby providing a punched card. The punched card is put into a large computer through a card reader, and an NC tape is automatically prepared through a tape preparing unit connected to said computer.
In automatic programming, the NC language is so difficult as to require an excellent programmer. Further, part programming is difficult. And, a large computer has to be used.
In brief, automatic programming requires an excellent programmer and since it seeks to solve the problems associated with various processes and operations by aid of software, it requires medium- and large-sized computers, which are more expensive then the NC machine.